Nutritional properties of tempeh flour from quality protein maize (Zea mays L.)

The objective of this investigation was to evaluate physico-chemical and nutritional properties of tempeh flour from a quality protein maize (QPM). In comparison to untreated QPM, the QPM tempeh flour showed a higher (P?0.05) gelatinization temperature (81.7 vs 73.9 °C), and resistant starch (4.24 vs 1.9 g/100 g dry flour), and a lower (P?0.05) gelatinization enthalpy (1.94 vs 2.74 J/g) and total starch content (56.9 vs 62.6 g/100 g dry flour). The essential amino acids (EAAs) content of raw QPM flour was improved by the solid-state fermentation process. The contents of His, Ile, and Leu increased (P?0.05) in 0.81, 0.52, and 1.46 g/100 g protein, respectively. The total sulphur and total aromatic EAAs increased (P?0.05) in 0.55 and 3.45 g/100 g protein, respectively. In untreated QPM flour, the first and second limiting EAAs were Lys and Trp, with EAAs score of 0.72. First and second limiting EAAs in QPM tempeh flour were Trp and Lys, with an EAAs score of 0.84. The SSF process increased (P?0.05) nutritional indicators as follows: protein efficiency ratio (PER) from 1.78 to 2.10, calculated PER from 1.43 to 1.74, and protein digestibility corrected amino acid score from 0.55 to 0.83. It is concluded that based mainly on its nutritive value, fermented flour may be considered for the fortification of widely consumed cereal-based food product (tortillas, bread, cookies, atoles).     

Enzyme activity during germination of different cereals: A review

The germination process increases enzymatic activity. However, this does not occur in the same way in all cereals. It depends on the type of enzyme, the cereal, and the conditions of germination. During germination, most enzymes are localized in the aleurone layer and the scutellum. Some of them, such as xylanases, proteases, and β-glucanases, are also localized in the endosperm while β-glucanases and lipases have been identified in the embryo. The maximum activity of the enzymes in most cereals start from day 4 of germination. Germination allows the hydrolysis of macromolecules and compounds like β-glucans and phytic acid. In cereals, starch is the component that presents the most morphological changes. Germination mobilizes and increases the activity of some enzymes. Temperature, steeping time, and variety are determining factors in the activation time. At higher temperatures, the enzymatic activation is generally faster; however, there are some exceptions. The use of germination could be a promising resource for modifying grain properties and increase enzymatic activity; also, this process is simple and economical.     

Resistant Starch Content and Structural Changes in Maize (Zea mays) Tortillas During Storage

Storage of maize products such as tortillas may cause starch retrogradation and lead to resistant starch (RS) formation. This study was carried out to determine if storage of maize tortillas under refrigerated conditions enhanced RS content and/or modified RS structure. Improved Costeño variety maize grain was nixtamalized and processed into tortillas which were stored for five and ten days at 5°C. Total resistant starch (TRS) and retrograded resistant starch (RRS or RS3) contents were determined on raw and nixtamalized maize grain and tortillas stored for zero, five and ten days. Differential scanning calorimetry (DSC), X‐ray diffraction (XRD) and near‐infrared (NIR) spectroscopy were use to evaluate structural changes in retrograded resistant starch isolated from each sample type. Total starch content was 67 ± 1.5% for all samples, TRS ranged from 3.3% in the raw grain at 7.2% in tortillas stored for ten days, while RRS starch content ranged from 0% in the raw grain to 3.2% in tortillas stored for ten days. DSC showed endothermic transitions corresponding to amylopectin and amylose retrogradation, at 31.9 and 139.7°C in RRS from tortillas stored for five days, and at 47.9 and 146°C in RRS from tortillas stored for ten days. These values agreed with the higher total RS content recorded after prolonged storage. XRD revealed a starch crystallinity of 13.7% in tortillas stored for five days and 15.3% in those stored for ten days. NIR spectroscopy analysis showed evidence of structural changes in polymeric order that were more pronounced in RRS of tortillas stored for ten days, due to increase in crystalline region.     

Effect of Soybean 7S Protein Fractions, Obtained from Germinated and Nongerminated Seeds, on Dough Rheological Properties and Bread Quality

Germinated soybean flour has been proposed for use in bread making as a product to improve bread quality when small amounts are added to wheat flour. However, it is not clear which soybean components promote this action, and how these components may influence bread quality. The aim of this work was to evaluate the effect of the addition of soybean 7S protein fraction obtained from germinated and nongerminated seeds in dough rheological properties (farinographic and extensographic) and bread quality, including loaf volume, texture (firmness, compression force, resilience), colour (L*, a*, b*), crumb grain structure (cell density, mean cell area, shape factor), and consumer acceptance (sensory analysis). Results showed that this protein fraction just slightly affects bread quality, since no significant changes (P > 0.05) on bread volume and texture were obtained. Only crust and crumb colour were affected in a small amount, and a coarser crumb structure was also observed when adding 7S protein obtained from germinated soybean at its highest concentration. As the proportion of protein increased in the flour, both kinds of 7S fraction (germinated and nongerminated) were related to the increment in water absorption, as well as to the increment in extensographic maximum resistance to extension, specifically when adding 7S protein obtained from nongerminated soybean seeds. These results showed that the 7S soybean protein, as obtained in this work, is not related to the reported loaf bread quality improving effect of this legume when it is added in small quantities.     

The Composition,Rheological and Thermal Properties of Tajonal (Viguiera Dentata) Mexican Honey

Samples of Tajonal honey (Viguiera dentata) from Yucatan, Mexico with different moisture contents were studied for their physicochemical, crystallization, rheological, and thermal characteristics. The presence of crystals changed the flow behavior from Newtonian to non-Newtonian. A characteristic glass transition temperature (Tg') was found for each sample, and it was observed to be dependent of the initial moisture content but independent of the storage period. The temperature and latent heat of fusion were not affected by the crystallization phenomenon, while both the moisture content and the glucose/water ratio were useful indexes for crystal growth in honey. Crystallization process can be controlled by harvesting the product with higher moisture contents without exceeding the limits established by international regulations.     

Synthesis and characterization of semi‐interpenetrating networks based on poly(dimethylsiloxane) and poly(vinyl alcohol)

Semi‐interpenetrating networks (Semi‐IPNs) with different compositions were prepared from poly(dimethylsiloxane) (PDMS), tetraethylorthosilicate (TEOS), and poly(vinyl alcohol) (PVA) by the sol‐gel process in this study. The characterization of the PDMS/PVA semi‐IPN was carried out using Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and swelling measurements. The presence of PVA domains dispersed in the PDMS network disrupted the network and allowed PDMS to crystallize, as observed by the crystallization and melting peaks in the DSC analyses. Because of the presence of hydrophilic (? OH) and hydrophobic (Si? (CH₃)₂) domains, there was an appropriate hydrophylic/hydrophobic balance in the semi‐IPNs prepared, which led to a maximum equilibrium water content of ～ 14 wt % without a loss in the ability to swell less polar solvents. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Structural and farinographic changes during mixing of a yeast sweet dough

Sweet dough requires longer mixing time than salty or white pan bread doughs to reach a developed stage. Although many studies have dealt with the effect of mixing time on dough, few have referred to yeast sweet doughs. The aim of this study was to evaluate if the changes in dough microstructure during different stages of mixing were the same between sweet pan bread and white pan bread, using as control a flour water system. Scanning electronic microscopy (SEM) and some bread characteristics were used as evaluation parameters. Doughs were prepared in a Brabender Farinograph instrument. Different mixing times were used for each formulation, which correspond to common farinographic parameters such as: arrival time, peak time, departure time, etc. Farinographic consistency was evaluated at those times. Results showed that sweet dough farinogram was quite different from those obtained from the other two samples; it starts with a low consistency value (260 BU), and after 8 min of mixing it began to increase until almost reaching the 500 BU line; then the graphic follows the classical curve. Larger products were obtained from arrival time to departure time for both formulations. SEM showed that as mixing proceeds the dough structure opens, changing its appearance from a compact structure at the beginning to a very open one at the end of the mixing process. SEM also showed that the process of mixing is the same for the two samples and control; however, the time needed to reach each stage was different among samples. Farinogram can be used to get information about mixing behavior of yeast sweet doughs. The study of mixing can be easier using sweet dough formulations because it was possible to get more points between the onset of mixing and full dough development, and the process was very similar no matter the formulation.     

Effect of baking method on some characteristics of starch in pound cake crumbs

BACKGROUND: The effect of the baking process (microwave versus conventional oven) on some starch characteristics of pound cake was evaluated. Proximal chemical analysis, total resistant starch (RS), retrograded resistant starch (RS3), differential scanning calorimetry (DSC), and X‐ray diffraction (XRD) were evaluated. Pound cake, one of the major products of Mexico's bread industry, was selected for analysis because the high moisture and fat content in the beaten dough might reduce the quality defects often associated with microwave baking. RESULTS: Crumbs from microwave‐baked pound cakes contained lower moisture than crumbs from conventionally baked pound cake. Lower RS was observed in fresh microwave‐baked than conventionally baked pound cake. RS3 increased significantly in conventionally baked products stored for 8 days at room temperature, whereas slightly lower changes in RS3 were observed in the microwaved product. DSC revealed less gelatinisation in microwaved pound cake which is related to limited water availability during the microwave heating process. The crystallinity peaks present in conventionally baked pound cake might be associated with RS3 content; the resistant retrograded starch formed during storage, is reflected in the XRD pattern. CONCLUSION: Microwave‐baked pound cake crumbs showed less gelatinisation than conventionally baked pound cake crumbs. Copyright © 2007 Society of Chemical Industry     

Extrusion of banana starch: characterization of the extrudates

Extrusion of banana starch was carried out for obtaining extrudates with functional and digestibility characteristics. Experimental design with temperature, screw speed and moisture content as independent variables produced 20 experiments that were studied using response surface methodology to discover the effect of these variables on resistant starch content, water absorption index and water solubility index. The amylose content was 37.4% with high resistant starch (RS) content in the ungelatinized sample, which decreased when banana starch was gelatinized (1.9%). Extrudate samples had a higher RS content than the gelatinized native starch, showing that the extrusion process increased RS content of native starch due to starch depolymerization and during cooling of extrudates those linear chains form an arrangement that cannot be hydrolyzed by α‐amylase. The response surface regression model fitted to experimental results of resistant starch showed good determination coefficient (84%). During model validation for RS, the model explains the experimental results up to 90%. Response surface showed that water absorption index values were high when the temperature, moisture content and screw speed were also high; water solubility values were not affected by screw speed, and both temperature and moisture content had a quadratic effect. Cylindrical structures were observed in powders where RS was present and as RS level increased the cylinders became coarser. Copyright © 2006 Society of Chemical Industry     

Operation Policies through Dynamic Programming and Genetic Algorithms,for a Reservoir with Irrigation and Water Supply Uses

Water Resources Management - In this study, operation policies were obtained for a reservoir in Michoacán, Mexico, used for irrigation and domestic water supplies. The main purpose of these...